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United States Patent |
5,327,123
|
Heimann
,   et al.
|
July 5, 1994
|
Traffic control system failure monitoring
Abstract
A traffic control system for use at a roadway intersection, the system
including traffic control lights, a light flasher structure, and a
plurality of load switches electrically coupled with the lights via relay
structure to which the flasher structure is connected, the load switches
having inputs, and a controller connected with the load switches for
controlling normal operation of the lights and flashing of one or more of
the lights by the flasher structure in the event of a system malfunction
comprising a microprocessor operatively connected with the load switches,
flasher, and relay structure to monitor the system for detecting a
malfunction event, for recording the detected malfunction event, and for
transmitting the malfunction detection to another location; and
verification structure at the other locations for i) receiving the
transmitted malfunction detection, ii) verifying the event, and iii)
initiating malfunction corrective action; whereby the corrective action in
the system may be initiated without removing control by the controller of
the operation of the traffic control lights at the intersection.
Inventors:
|
Heimann; Kenneth R. (Corona, CA);
Chu; Hien T. (Carson, CA)
|
Assignee:
|
Traffic Sensor Corporation (Corona, CA)
|
Appl. No.:
|
872770 |
Filed:
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April 23, 1992 |
Current U.S. Class: |
340/916; 340/641; 340/912; 340/931 |
Intern'l Class: |
G08G 001/07 |
Field of Search: |
340/916,912,931,641,642
364/436
|
References Cited
U.S. Patent Documents
2166721 | Jul., 1939 | Jeffers | 340/931.
|
3596239 | Jul., 1971 | Hata | 340/931.
|
3629802 | Dec., 1971 | Clark et al. | 340/931.
|
3648233 | Mar., 1972 | Clark | 340/931.
|
3778762 | Dec., 1973 | Jarko et al. | 340/931.
|
3902156 | Aug., 1975 | Hill | 340/931.
|
4024528 | May., 1977 | Boggs et al. | 340/310.
|
4135145 | Jan., 1979 | Eberle | 340/931.
|
4383240 | May., 1983 | Staats, Jr. | 340/915.
|
4566008 | Jan., 1986 | Powers et al. | 340/941.
|
Other References
"Conflict Monitors", TS-1, Jan. 1983, Section 6, pp. 45-46, Nema Standard.
|
Primary Examiner: Crosland; Donnie L.
Attorney, Agent or Firm: Haefliger; William W.
Claims
We claim:
1. In a traffic control system for use at a roadway intersection, the
system including traffic control lights, a light flasher means for
effecting light flashing, relay means for electrical coupling, and a
plurality of load switches electrically coupled with said lights via said
relay means to which said light flasher means is connected, said load
switches having inputs, and a controller connected with said load switches
for controlling normal operation of said lights and flashing of one or
more of said lights by said light flasher means in the event of a system
malfunction, the combination comprising
a) a microprocessor operatively connected with the said load switches, said
light flasher means, and said relay means to monitor the system for
detecting a malfunction event, for recording the detected malfunction
event, and for transmitting the detected malfunction event to another
location,
b) and verification means at said other location for
i) receiving said transmitted malfunction detection,
ii) verifying said event, and
iii) initiating malfunction corrective action,
c) whereby said corrective action in said system may be initiated without
removing control by the controller of said operation of the traffic
control lights at said intersection.
2. The combination of claim 1 wherein said load switches have output sides
and said microprocessor is coupled to the output sides of said load
switches to receive AC signals from said load switches which are compared
with selected input signal levels to determine malfunction events, there
being means for providing said selected input signal levels.
3. The combination of claim 2 including a comparator coupled to said load
switches and having inputs from said load switches, and including a
reference voltage source, said comparator receiving input from said
reference voltage source.
4. The combination of claim 1 including flash transfer relay means coupled
to said light flasher means, and wherein said microprocessor includes
circuit means for transferring traffic signal lamp loads from the load
switches to the light flasher means under substantially no-load conditions
whereby arcing of the flash transfer relay means is suppressed.
5. The combination of claim 1 wherein said controller supplies control DC
signals having signal levels, the load switches have input sides coupled
to the controller to receive said control DC signals, and the
microprocessor includes means coupled to the input sides of the load
switches to measure said DC signal levels.
6. The combination of claim 2 including saturable core reactor means
coupled to said load switches.
7. The combination of claim 6 including signal integration means coupled to
the output side of said reactor means for representing the current for a
resistive load.
8. The combination of claim 5 wherein said load switches have output sides
and said microprocessor is coupled to the output sides of said load
switches to provide AC signals which are compared with selected input
signal levels to determine malfunction events and including hold-off
circuitry means coupled to said load switches and said light flasher means
to hold of switching of loads to the lights via the light flasher means to
a selected low-level time during an AC cycle associated with an AC signal.
9. The combination of claim 2 wherein said microprocessor is coupled to an
output side of said flasher means to enable determination of malfunction
of said flasher means.
10. The combination of claim 1 wherein the load switches have output sides
and said microprocessor has coupling to the output sides of the load
switches to provide AC load current measurements enabling determination of
malfunction events.
11. The combination of claim 10 wherein said coupling includes a saturable
core reactor.
12. The method of operating the system of claim 1 including
i) causing the microprocessor to establish different signal thresholds,
including
x.sub.1) a 0 volt reference, whereby a 0 level signal crossover detector is
provided to verify that the measured traffic signal lamp voltage is in
phase with the AC line voltage and is not shorted to another phase
voltage,
x.sub.2) a negative voltage reference, for measurement of only the negative
half cycle of traffic signal voltage, and for determination as to whether
its amplitude is sufficient to drive a traffic signal lamp,
x.sub.3) a positive voltage reference for measurement of only the positive
half cycle of traffic signal voltage
whereby load current can be measured without use of current sensor loops.
13. In a traffic control system for use at a road intersection, the system
including traffic control lights, a light flasher means for effecting
light flashing, relay means for electrical coupling, and a plurality of
load switches having output sides electrically coupled with the lights via
said relay means to which said light flasher means is also connected, and
a controller connected with said load switches for controlling normal
operation of said lights and flashing of one or more of said lights by
said light flasher means in the event of a system malfunction, the
combination comprising
a) a signal monitor means coupled to said light flasher means via said
relay means, and also coupled to said load switches, whereby the signal
monitor monitors voltage at said output sides of the load switches,
b) each load switch having three DC inputs, three corresponding outputs,
one output being turned ON in response to application of a DC ground to
the corresponding DC input,
c) a voltage summing circuit coupled to the input of each load switch, said
circuit including three interconnected resistors respectively in series
with said DC inputs, and said circuit coupled to said signal monitor
means,
d) the voltage summing circuit including three diodes respectively
connected in series with the three resistors to prevent the DC inputs from
feeding energy to the signal monitor means when said inputs are in
off-state,
e) the signal monitor means including an additional resistor coupled to a
stable reference voltage,
f) said additional resistor and the three resistors in said voltage summing
circuit forming a voltage divider when a DC output from the load switch is
selected by the controller, to allow determination of which DC input is
ON, at a particular load switch.
14. The combination of claim 13 including an A to D converter in said
monitor, and having its output coupled to said voltage divider between
said additional resistor and said three resistors, said three resistors
having different resistance values and connected in parallel with said
additional resistor.
15. The combination of claim 13 wherein AC field wire voltages are supplied
to power said traffic control lights and 24 volt DC input signals are
supplied from a power supply to the load switches, and wherein said
microprocessor includes conflict monitor means for measuring said AC field
wire voltages and said i24 volt DC input signals and for comparing said AC
voltages and said DC inputs to determine malfunction.
16. The combination of claim 15 wherein the conflict monitor includes
circuit means for transferring traffic signal lamp loads from the load
switches to the flasher means under substantially no-load conditions
whereby arcing at the relay means is suppressed.
17. The combination of claim 15 wherein said monitor means includes
internally or externally located load sensing switches, or current sensing
means, to measure load currents supplied as a result of said 24 volt DC
inputs.
18. In a traffic control system for use at a road intersection, the system
including traffic control lights, a light flasher means for controlling
light flashing, relay means for electrical coupling, and a plurality of
load switches electrically coupled with the lights via said relay means to
which said light flasher means is also connected, and a controller
connected with said load switches for controlling normal operation of said
lights and flashing of one or more of said lights by said light flasher
means in the event of a system malfunction, the combination comprising
a) a signal monitor means,
b) each load switch having three DC inputs, three corresponding outputs,
one output being turned ON in response to application of a DC ground to
the corresponding DC input, there being means to allow determination of
which DC input is ON, at a particular load switch,
c) there being power supply means connected to the load switches, and AC
field wire voltages being supplied to power said traffic control lights
and 24 volt DC input signals are supplied from said power supply means to
the load switches, and wherein said microprocessor includes conflict
monitor means for measuring said AC field wire voltages and said 24 volt
DC input signals and for comparing said AC voltages and said DC inputs to
determine malfunction.
19. The combination of claim 18 wherein the conflict monitor includes
circuit means for transferring traffic signal lamp loads from the load
switches to the light flasher means under substantially no-load conditions
whereby arcing at the relay means is suppressed.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to traffic control systems, and more
particularly to improvements in monitoring of traffic signal lights for
proper operation at controlled roadway intersections.
The present art in the traffic control system uses a controller unit that
energizes load switches that drive the signal lamps through a flash
transfer relay. In the event that a conflicting signal should arise, a
conflict monitor can actuate the relay to transfer the lamp loads to the
flasher module.
The conflict monitor measures the traffic signal lamp voltages by
converting the AC to DC, enabling a gate which then indicates whether the
voltage is present or not. If two signal lamp voltages are ON at the same
time in conflicting directions, for instance eastbound and northbound,
traffic green signal lights ON, setting up a potential hazard; the
conflict monitor will drop or de-energize the flash transfer relay,
putting the lamp loads under the control of the flasher, thus putting the
intersection into flash.
Prior art has defined a traffic control system as consisting of a traffic
controller unit for the purpose of providing 24 volt DC input signals to
one or more load switches used to turn traffic signal lamps ON. A conflict
monitor device is used to monitor the presence of proper alternating
current field wire voltages supplied to power the traffic signal lamps.
When improper AC voltages exist, the conflict monitor causes an
electro-mechanical relay to transfer, which in turn causes the high
current capacity flash transfer relay to remove lamp power from the load
switches and to connect the lamp power to a flasher unit, which causes the
traffic signal lamps to flash ON and OFF.
In addition to monitoring the AC voltages on the outputs of load switches,
the conflict monitor checks for the presence of a 24 volt DC output from
the power supplies used by the traffic controller to produce 24 volt DC
signals for turning the load switch outputs ON. The 24 volt DC signals
supplied from the traffic controller to each of the individual load switch
circuits have not previously been monitored within the conflict monitor or
the controller unit. A proposed improvement to NEMA traffic control device
standards, proposed standard TS2 for future design, would require
communication between the traffic controller and the conflict monitor with
information sent regarding the programmed traffic controller 24 volt DC
signal status, but would not provide a measurement of the 24 volt DC
signals actually present at the load switches. U.S. Pat. No. 4,383,240
describes monitoring of DC logic signals, storage, and display of same,
along with output status conditions.
There is need for improvements in the control of signal flashing and in the
detection and handling of system malfunctions, including that of signal
lamps (bulbs), and for simplification of system apparatus and functions.
SUMMARY OF THE INVENTION
It is a major object of the invention to provide an improved system meeting
the above needs.
The environment of the invention comprises a traffic control system for use
at a roadway intersection, the system including traffic control lights, a
light flasher means, and a plurality of load switches electrically coupled
with the lights via relay means to which the flasher means is connected,
the load switches having inputs, and a controller connected with the load
switches for controlling normal operation of the lights and flashing of
one or more of the lights by the flasher means in the event of a system
malfunction.
In this environment, the invention provides:
a) a microprocessor operatively connected with the load switches and relay
means to monitor the system for detecting a malfunction event, for
recording the detected malfunction event, and for transmitting the
malfunction detection to another location,
b) and verification means at the other locations for
i) receiving the transmitted malfunction detection,
ii) verifying the event, and
iii) initiating malfunction corrective action,
c) whereby the corrective action in the system may be initiated without
removing control by the controller of the operation of the traffic control
lights at the intersection.
It is another object of the invention to provide means to monitor AC field
wire voltages supplied via load switches to power the traffic control
lights, and means to monitor DC inputs of the load switches to enable
determination, for any load switch, which of three (red, yellow and green
signals) DC inputs is ON.
As respects such DC monitoring, the invention provides:
a) a signal monitor means,
b) each load switch having three DC inputs, three corresponding outputs,
one output being turned ON in response to application of a DC ground to
the corresponding DC input,
c) a voltage summing circuit coupled to the input of each load switch, the
circuit including three interconnected resistors respectively in series
with the DC inputs, and the circuit coupled to the signal monitor means,
d) the voltage summing circuit including three diodes respectively
connected in series with the three resistors to prevent the DC inputs from
feeding energy to the signal monitor means when the inputs are in
off-state,
e) the signal monitor means including an additional resistor coupled to a
stable reference voltage,
f) the additional resistor and the three resistors in the voltage summing
circuit forming a voltage divider when a DC input to the load switch is
selected by the controller, to allow determination of which DC input is
ON, at a particular load switch.
As respects the reference to AC voltage monitoring, it is an object of the
invention to provide conflict monitor means to sequentially compare the AC
voltages with reference voltage in the monitor, the monitor also operating
to provide DC signal monitoring, as referred to. Thus, the conflict
monitor may comprise a module coupled to the input and output side of each
load switch, to function as described.
It is another object to provide input monitor means with circuit means for
transferring traffic signal lamp loads from the load switches to the
flasher means under substantially no-load conditions whereby arcing at the
flash transfer relay means is suppressed.
These and other objects and advantages of the invention, as well as the
details of an illustrative embodiment, will be more fully understood from
the following specification and drawings, in which:
DRAWING DESCRIPTION
FIG. 1 is a system block diagram;
FIG. 2 is a block diagram showing AC field wire voltage monitoring;
FIG. 3 is a block diagram showing monitoring of DC voltage input levels to
load switches;
FIG. 3a is a circuit diagram;
FIG. 4 is a flasher circuit diagram;
FIG. 5 is a load switch circuit diagram;
FIG. 6 is an analog board circuit diagram;
FIG. 7 is a block diagram showing details of the conflict monitor seen in
FIG. 1;
FIG. 8 is a "hold-off" circuit diagram;
FIG. 9 is a circuit diagram showing analog board coupling between load
switch inputs and the conflict monitor;
FIG. 10 is a circuit diagram showing use of saturable care reactors in the
load switches;
FIGS. 11(a), 11(b), and 11(c) are wave forms;
FIG. 11(d) is a circuit diagram showing integration of circuit sensor
signals, as represented in FIG. 11 (c);
FIGS. 12(a), 12(b), and 12(c) are wave forms; and 12(d) is a comparator
circuit; and
FIGS. 13(a), 13(b),and 13(c) are wave form diagrams, and 13(d)is a
comparator circuit.
DETAILED DESCRIPTION
In FIG. 1, a traffic controller is indicated at 10, as having output at 11,
connected at 12-16 with load switches 17-20. Such switches have outputs at
21-24 connected at 25-29 with flash transfer relay means 30, which is in
turn connected at 31-36 with traffic control light units 37-40. The latter
are normally located at different corners of a roadway intersection. When
a system malfunction occurs, red lights in units 37-40 are placed in a
flashing mode. This is accomplished by the high current capacity relay
means 30, which receives a flash initiating signal from a conflict monitor
41, via connection 42. The relay removes power transmission from the load
switches to the lights (the four load switches normally connected via the
relay to the respective four lights), and connects power transmission from
the flasher circuit 43 to all light units.
The conflict monitor 41 is shown as operatively connected with the load
switches 17-20, as via bus 44, Load Management System (LMS) analog board
45, bus 56 and connections 47-50, whereby the monitor 41 measures the
presence or absence of predetermined or selected AC field wire voltages at
the outputs of the switches 17-20, for example appropriate level AC
voltage level supply to the light units from the load switches. Also, the
conflict monitor 41 monitors the DC voltage from the controller that is
used to turn each load switch output ON. If the DC voltage from the
controller is not selected, but the output from the load switch is ON or
vice versa, the conflict monitor determines that a malfunction has
occurred and initiates corrective action.
Such measurements by the conflict monitor may effectively be made by
comparing the AC voltage level with a selected level, as in a comparator;
and by comparing the DC voltage level with a selected (24 volt) level, as
in a comparator. Such measurements are made by the conflict monitor while
measuring the current actually drawn by the signal lamp loads at the light
units as via bus 44 connected with output leads 25-28. Bus 44 provides DC
voltage status of the load switches 17-20 to the monitor 41; whereas bus
52 provides AC voltage information to the monitor.
LMS circuit 44 is not only connected at 47-50 and via board 45 with the
load switches, but also with the flasher circuit 43 via connector 55. The
LMS and conflict monitor 41 respond to a malfunction, such as dropping of
the AC output voltage from a load switch below a threshold, to cause the
relay means 30 to decouple from the load switches, and couple to the
flasher unit, at a non-load condition during the AC cycle. This is
extremely beneficial, as the electro-mechanical flash transfer relays used
at 30 for load switching normally are required to transfer relatively high
electrical currents; and if switching is done with random timing during
the AC cycle, arcing can likely occur, causing damage to the load switches
17-20, to the flasher circuit 33, and other devices. Note also that the
monitor 41 enables malfunctioning corrective action to be initiated
without removing control by controller 10 of operating of the traffic
signal lights 37-40. This allows the traffic intersection to be operated
(by the lights) in a highly efficient manner, to enable increased
vehicular traffic flow and correspondingly reduced vehicle fuel
consumption.
FIG. 2 shows in further detail the manner in which the conflict monitor
measures the output voltages from the load switches and compares these
with a reference. Load switch 17 has connections 25a, 25b and 25c with
relay switches 30a, 30b and 30c; and the latter are connected at 33a, 33b
and 33c with the red, yellow and green lights of light units 37, as shown.
Likewise, load switch 18 has connections 26a, 26b and 26c with relay
switches 30d, 30e and 30f; and the latter are connected at 38a, 38b and
38c with the red, yellow and green lights of light unit 38. Typically, one
relay 30 is used (see one armature 30k solenoid controlled at 30j. In one
position, it allows connections from 25a, 25b, and 25c to light inputs at
37a, 37b, and 37c, as shown; in another position of 30k, it connects only
red light inputs 37a, 38a, etc., with the flasher 43, as via leads 43d and
43e.
Outputs from lines 25a-25c are connected via lines 47a, 47b and 47c with a
multiplexer amplifier 60, via attenuator 61, in monitor 41 (which may be
considered to include LMS board 45); and outputs from lines 26a-26c are
connected via lines 48a, 48b and 48c with 60 and 61. The multiplexer
applies the voltages on 47a-47c and 48a-48c, one at a time to the
comparator 62, where they are compared with a reference voltage applied at
63 to the comparator. That reference voltage is supplied and controlled
via CPU 64, as via isolator 65 and digital to analog converter 66. The
comparator output at 67 is fed via isolator 68 to the CPU, for processing
to determine whether it exceeds (for any of the AC inputs at 47a-47c and
48a-48c) a selected threshold level, thereby indicating a malfunction.
Attenuator 61 is controlled by the CPU via line 69 and isolator 70
(buffer). A "watch dog" signal is transmitted at 71 by the CPU to monitor
proper operation of the CPU.
The conflict monitor CPU may be programmed to monitor for occurrence of
malfunctions and to react to them as a fault as has traditionally been the
practice in the industry where the intersection is removed from actuated
control by the controller 10 and put into flashed control by the flasher
43, or to react to malfunctions as a message where the occurrence of the
malfunction is recorded, stored, and, if desired, transmitted to other
equipment without removing control of traffic from the traffic controller
10. The benefits of this are increased traffic flow, reduced congestion,
reduced fuel consumption, and reduced vehicle emissions (pollution).
Separate memory records may be used for the purpose of storing faults and
messages. See record means 64a.
The LMS also logs into a memory record the occurrence of user-inputted and
traffic control system-initiated changes in the operation of the load
management system. This information is recorded and stored in a memory
record, as at 64b, which may be separate from the fault and message memory
records. Information logged relates to times and dates, and nature of
changes in the monitoring operation, and to the information stored in
other memory records, such as fault memory and message memory.
Referring now to FIGS. 3 and 5, the means to monitor the DC circuit levels
at the inputs to the load switches will now be described. Each load switch
has three inputs, as well as three outputs, previously referred to, as at
25a-25c and 26a-26c. FIGS. 3 and 5 show load switch 17 DC inputs at
80a-80c, and analog channel 80d connected to 80a-80c, and also connected
to the LMS, including analog board 45 and multiplexer 83. The latter
delivers those three analog circuit levels, serially, via connector 84 to
an A to D converter 85 in monitor 41. FIG. 6 illustrates such a board 45
in greater detail. (Parallel delivery of circuit levels could be
employed.)
Refer now to FIGS. 3a and 5 showing the three DC input levels A, B and C
fed to the converter 85 (in 41) via the three resistors 86, 87 and 88, to
summing junction 89, the resistors having different values. See FIG. 3a
for representative values. Three diodes 90-92 are in series with the
respective resistors to prevent DC inputs from feeding energy into the
board 45 and monitor 41. Inside the monitor 41 the analog DC signal
obtained is tied at 93 to a stable reference voltage 94, through a
resistor 95. The latter, plus the three resistors 86-88 in the load switch
17, form a voltage divider when a DC input from the load switch is
selected by the controller. A filter comparator is shown at 96. By
converting the analog DC status signal to a digital signal, the signal
monitoring unit can determine which resistor (86, or 87, or 88) in the
load switch is included in the divider network; and this in turn allows
determination by the monitor of which DC input (80a, 80b or 80c) is ON, at
a particular load switch. See also the detailed circuitry in FIG. 9.
As described, the load switch has three associated signals: DC input A, DC
input B, and DC input C which represent three inputs from the controller
unit to the corresponding DC inputs A, B and C. To turn on an output, the
corresponding input requires a DC low voltage. When nothing is selected or
when there is no connection between the conflict monitor and the load
switch, the pull-up resistor, R4, at 95, sets the A to D value to 5 volts
DC (assuming that voltage reference is 5 volts). When an input is
selected, the corresponding resistor inside the load switch and resistor
95 form a divider network. This network will give different A to D values
depending on which resistor is included in the network. The table below
shows the different A to D values based on the different input selected.
Voltage reference is assumed to be 5 volts DC.
______________________________________
INPUT
SELECTED RESISTORS IN NETWORK
A TO D VALUE
______________________________________
None R4 5.00 volts
A R1, R4 1.56 volts
B R2, R4 2.38 volts
C R3, R4 3.23 volts
A, B R1, R2, R4 1.16 volts
A, C R1, R3, R4 1.33 volts
B, C R2, R3, R4 1.88 volts
A, B, C R1, R2, R3, R4 1.03 volts
______________________________________
Referring to FIG. 7, it shows in more detail the functional blocks of the
conflict monitor for measuring AC signal voltages supplied to the signal
lights or lamps, and also as referred to above. It incorporates for each
light channel (red, yellow and green) use of a reference voltage, as at 63
(for example) that can be changed by the DAC 66, under control of the
microprocessor CPU 64.
The invention enables changing of input circuitry to measure traffic signal
lamp voltages using different microprocessor set thresholds at different
times. In doing this, several benefits are achieved:
a) By setting the reference to 0 volts, the input circuitry becomes a zero
crossover detector which can be used to verify that the measured traffic
signal voltage is in phase with the AC line voltage and is not shorted to
another phase voltage (for instance street lights).
b) Setting the reference to a negative voltage allows the measurement of
only the negative one half cycle. This then allows the microprocessor to
determine if the negative half cycle of traffic signal voltage is present
and of sufficient amplitude to drive the traffic signal lamp.
c) Setting the reference to a positive voltage allows for the measurement
of only the positive half cycle. This then allows the microprocessor to
determine if the positive half cycle of traffic signal voltage is present
and of sufficient amplitude to drive the lamp.
d) The determination or knowledge of the presence of a half wave signal
will allow the microprocessor to set different references for half wave
than for full wave traffic signal voltages. This is important because
conservation of power is often achieved by providing half wave rectified
voltages to traffic signals.
e) This technique is also used to measure the load resistance during the
OFF time, thus giving the microprocessor a method of testing for the
presence of, and for the amount of, the load. This provides a method for
measuring current which does not require the use of additional current
sensor loops.
The above additional information provided to the microprocessor can be used
to record when a malfunction occurs and to report to a central office
without having to put the intersection into flash. This makes it possible
for increased traffic flow, reduced fuel consumption and reduced down
time.
In FIGS. 12 (a)-(d), the microprocessor first sets up the reference to 0
volts DC and waits until a change of state occurs from 0 to 1 at the
output of the comparator 137. See 12(b). At the time the state changes,
the input is at 0.degree. in FIG. 12(a). Then the microprocessor sets up
the D to A for a reference into the comparator equal to the required
threshold of the positive half cycle. At this time, the output of the
comparator will change from 1 to 0. The microprocessor continues to
monitor the output for a state change from 0 to 1 within a time period
that does not exceed 1/2 the cycle time. If the states does change from 0
to 1, the positive threshold was reached. The microprocessor then sets up
the reference to 0 volts DC and waits until it sees a change of state from
1 to 0 at the output of the comparator. At the time the state changes, the
input is at 180.degree.. Then, the microprocessor sets up the D to A for a
reference into the comparator equal to the required threshold of the
negative half cycle. At this time, the output of the comparator will
change from 0 to 1. The microprocessor continues to monitor the output of
the comparator for a state change from 1 to 0 within a time period that
does not exceed 1/2 the cycle time. If the state does b change from 1 to
0, the negative threshold was reached. If it does not occur in less than
1/2 cycle time, the threshold was not reached. At this time, the
microprocessor will set the D to A to 0 volts DC and repeat this process
all over again looking for the 0.degree. point.
Should the positive or negative thresholds not be reached, the input is not
present. There will, however, always be a zero crossover due to leakage
current of the surge protection circuitry in the load switch. During the
time that there is no input present to a load switch circuit, the load for
the corresponding output can be measured by switching the input attenuator
OFF with an analog switch. This gives the effect of changing the range.
In FIG. 13(a) to 13(d), the microprocessor sets up the reference to 0 volts
DC and waits until it sees a change of state from 0 to 1 at the output of
the comparator 141. At the time the state changes, the input is at
0.degree.. Following this state change of 0 to 1, the microprocessor then
steps up the D to A for a reference into the comparator and looks for the
next state change from 1 to 0. At the time the state change from 1 to 0
occurs, the reference is greater than the input. Then, the microprocessor
continues to monitor the output of the comparator until the state changes
from 0 to 1. If the time has not passed 1/4 cycle time, the microprocessor
steps up the D to A for a reference into the comparator 141, and looks for
a state change from 0 to 1 just as before until 1/4 cycle time has passed.
At this time, the peak voltage is reached and the voltage measured is
proportional to the load resistance. This measurement can be made every
time that the load switch is turned OFF and can be compared to the
previous measurement, thereby permitting detection of load changes, such
as can be caused due to burning out of signal lamps.
This technique is especially beneficial because it can automatically
measure out-of-phase AC voltages. By gradually changing the reference
voltage and looking for the state changes at the output of the comparator,
the conflict monitor can determine where the peak of an input is, and in
turn, determines the out-of-phase angle of the input from the AC line
reference.
Referring to FIG. 8, it shows hold-off circuitry associated with each load
switch, also seen in FIG. 5, as referred to above.
As shown, at the time that a conflict is sensed and just before the flash
transfer relay is dropped, a signal is sent at 95 to the load switches
17-20 and flasher 43. This signal will momentarily turn them OFF (hold
off), as via circuits 110, during the time that the flash transfer relay
is dropped. This will prevent the flash transfer relay from burning its
contacts and possibly sticking, ensuring safe operation of the
intersection and ensuring the reliable operation of the flash transfer
relay.
Note connector at 95 (in the analog board) between monitor transistor 96
and current source means 97-99 in the load switch circuits 17, 18, and 19,
for this purpose.
The flasher circuitry 43 seen in FIGS. 1 and 8 is shown in detail in FIG.
4.
In FIG. 4, the driver logic supply 103, alternately selects either the
triac 104 or 105 to generate an output 104a or 105a. These outputs then
feed through the inputs of the opto-isolators 106 and 107. Two resistors
of different values 110 and 111 are connected to the respective outputs
from the opto-isolators 106 and 107, respectively. Resistors 108 and 109
provide pull-up to Vcc. When the output of triac 104 is turned ON, the
corresponding opto-isolator 106 is also turned ON. The resistors 109, 111,
and 110 form a network divider with analog channel out 112 being measured
through an A to D converter 116 with the pull-down resistor 113 and a
filter capacitor 114. When triac 105 is turned ON, opto-isolator 107 is
turned ON. Resistors 108, 110, and 111 form a different network divider
and give a different value of analog channel out 112. By monitoring the
analog channel out 112, the conflict monitor 41 can detect that the
flasher 43 is operating by observing the analog channel out 112 switching
from one level of voltage to another.
In FIG. 2, the relay armature 30k is connected to all the switch arms, to
simultaneously switch their positions in response to energization of
solenoid 30j. That solenoid is operated, via line 182, by a driver
associated with the CPU of monitor 41, when a malfunction event occurs,
thereby to cause disconnection of the load switches from the traffic
lights (as at 37 and 38), and to connect the flasher circuit 43 with the
traffic signal red lights, as is clear from FIG. 2. The same operation of
the relay 30, to produce red light flashing, occurs in the event the
microprocessor CPU itself malfunctions; for example, interruption of CPU
clock signals delivered at 186 to the watch dog circuit 71 causing the
latter to operate the solenoid 30j via line 183, to effect red light
flashing in the manner referred to.
In FIG. 4, the A and B outputs are fed to the relay 30, as via each of
lines 43d and 43e, seen in FIG. 2. The opto-isolator circuit 190 in FIG. 4
is also referred to in connection with the description of FIG. 8.
Each load switch and flasher contains a 0.degree. phase angle driver.
Simply stated, by using the load switch and flasher to switch the power,
damage due to current in-rush surges is brought to a minimum. This is
accomplished by sending a positive signal to all of the load switches and
flashers (FIGS. 4, 5 and 8) through the analog board before the flash
transfer relay is de-energized. In the load switch (FIG. 5), this signal
is capacitively coupled to a current regulator and for a short, controlled
period of time (one to five AC line cycles) the current regulator is
changed from a 20 ma current regulator to a 0 ma current regulator. This
current is not adequate to drive the opto-isolator, used within the load
switch to supply power to the signal lamps, and, in turn, for that period
of time will shut down of all the load switches. The flasher (FIG. 4) at
the same time receives the same hold-off signal. It is driven through an
opto-isolator where, on the AC line side, it is capacitively coupled to a
blinking input on internal logic; or it may instead be capacitively
coupled to a transistor that momentarily shorts the flasher DC supply
voltage that runs the internal logic. Either circuit will work, with the
end result being that the flash transfer relay and the load switches and
flasher are all saved from excessive current in-rush by ensuring that all
switching is done at the zero crossover time. This aspect of the invention
has applicability in fields other than traffic control, where solid state
relays are used in conjunction with electro-mechanical relays or magnetic
contactors.
The invention also enables circuit measurement in a simple, effective
manner through use of a saturable core reactor, or reactors, as shown at
100 in FIGS. 5, 10, and 11(d).
The illustrated reactor 100 is a toroid that is driven into saturation by
the current to be measured, i.e., the current being supplied to the load.
See line 25a. This approach is different and unique from traditional
current transformers in that current transformers are not driven into
saturation. The counter EMF generated by the saturable reactor of this
invention is then rectified at 110a and integrated at 101 to represent the
current for a resistive load and supplied at 102 as an analog circuit to
the LMS. These integrated voltages are not linear with respect to the
current and more sensitive for small loads than for large loads. The
present invention does not require that a linear measurement be made and
provides increased sensitivity at lower currents. This invention can be
employed to detect a partial or a complete loss in load, such as the loss
of a traffic signal lamp from a parallel string of lamps. A lamp out
detection may be accomplished by detecting a sudden drop in the current
supplied to the load.
A corresponding reactor 100' is used in the flasher for measurement of
current supplied to loading during flasher operation. See 101' and 102' as
in FIG. 4.
Considering the above, note that
Volt source=volt load+volt inductor
Voltage total=(R.times.I)=(L.times.di/dt)
with the voltage across the inductor equal to
V=L.times.di/dt,
where
V=voltage,
L=inductance,
di=change in current
dt=change in time
Ampere's Law
I=0.795.times.H.times.1.times.I/N,
where
I=peak magnetizing current in Amperes 0.795=1/(pi.times.0.4),
H=magnetizing force in Oersteds,
l=mean magnetic path length in cm,
N=number of turns in primary.
Simply stated from these equations, di is a constant derived from the fact
that H in Ampere's Law reaches a maximum value at the saturation of the
magnetic core. Therefore, the current I reaches a maximum value as well.
This I maximum defines di in the previous equation. Consider the case of a
small load where the applied voltage is a sine wave (FIG. 2). Some amount
of time, dt, is required in the case of a larger load. As dt increases,
voltage decreases. As dt decreases, voltage will increase. This voltage is
stepped up on the secondary winding of the toroid and is rectified and
integrated in order to be read as an analog voltage representing the
current drawn by the load.
There are several advantages:
1. Electrical isolation from the load is maintained.
2. The voltage measurement is non-linear, making it more sensitive at lower
currents. This has the effect of automatically changing the range of the
current measurement.
3. The current sensor does not have a voltage drop after the magnetic core
is saturated, resulting in less power loss from the load to the magnetic
core than with other techniques.
4. Surge protection is provided by this circuit because the maximum energy
that can be coupled to the secondary is the energy that is stored in the
core. The nature of this invention is that small amounts of energy are
stored. This assumes good isolation from the load.
5. Reduced size and cost from other current measurement techniques is
achieved due to the fact that a small core is required in order to
saturate the core.
This approach works well in applications requiring measurement of changes
in resistive load current, such as for detecting tungsten lamp outages in
traffic signal displays. Another advantage of this invention is that
manual calibration is not required. A microprocessor can be used without
the need to know what the actual value of the current is; it is only
necessary to know if the current has changed. This fact is extremely
useful in automatic measurement and reporting of load current changes such
as light bulb burn-out occurrences.
Faraday's Law:
B=(E.times.100,000,000)/(4.4.times.A.times.N.times.f),
where
B=maximum flux density in gauss,
E=voltage across core in volts,
A=core cross sectional area in cm squared,
N=number of turns on the primary,
f=frequency in hertz.
L=(0.4.times.pi.times.u.times.N.times.N.times.A)/(1.times.10,000,000),
where
L=inductance,
u=core permeability (u=B/H),
B=maximum flux density in gauss,
H=magnetizing force in Oersteds,
N=number of turns in primary,
A=core cross sectional area in cm squared,
l=means magnetic path length in cm.
The constants A, l and u are fixed in the selection of the core to be used.
Faraday's Law is used in determining a suitable core, and it is desirable
in the application of detecting traffic signal lamp losses to use a tape
wound core as opposed to other types for the following reasons:
1. The tape wound core does not have a distributive gap. A distributive gap
prevents saturation of the core.
2. Higher gauss levels (magnetic flux density) can be achieved. This
results in much more accurate measurement because the signal strength is
many times higher than with other types of toroid cores.
3. This application requires load current measurements on an alternating
current line. This is a low frequency application (50-60H.sub.z) making it
ideal for the tape-wound core which works well at lower frequencies than
other types of toroid core. Not nearly as many urns around the tape-wound
core are required to yield the same measured voltage, E, as would be
required using cores, other materials and construction.
SUMMARY
The LMS herein is used in traffic controller assemblies to monitor and
ensure the safety of intersection operation. The LMS incorporates the
signal monitor unit, which measures load currents to know when signal
lamps fail; monitors and compares controller 24 volt DC driver signals
with load switch outputs to identify precisely which equipment fails;
continuously monitors flasher unit outputs before "flash" operation of the
intersection is required to verify that the flasher unit will perform when
the lamp loads are transferred to it; and eliminates electrical voltage
and current transients from being generated by flash transfer relays to
prevent their destruction as well as that of other cabinet electronics.
Special load sensing switches measure load current permitting detection of
the loss of solid state and fiberoptic signals as well as field wire
shorts. Load current measurements are sent to the monitor using a simple
harness and no cabinet rewiring or modification is necessary. With the
harnessing, the signal monitor unit is also provided with controller 24
volt DC driver signal status, which is compared with load switch outputs
to confirm proper operation of traffic signals. This permits
identification of equipment which malfunctions saving valuable maintenance
personnel and service equipment time. The simple harnessing used also
connects the SMU (i.e., monitor) with the flasher units so that their
outputs may be continuously monitored for proper operation before they
need to control the intersection. Failure of flasher units as well as all
other information stored in the SMU can be communicated to another
location via modem or RS232 connections or retained within internal memory
for retrieval when a field service person arrives. A convenient "MESSAGE"
indicator 64c calls attention to changes in recorded information and to
needed maintenance.
When flash transfer relays are required to transfer signal lamp loads to
flasher units, generation of high voltage and high current transients
caused by arcing of contacts is avoided. This prevents damage to
electronic equipment within the controller assembly and to flash transfer
relay contacts such that their replacement is virtually eliminated.
Sensing of load currents and 24 volt DC driver signals can be performed
outside of the load switches and flashers, such that the simple harnessing
described to connect load switches to the monitor is eliminated. The
sensing of load currents and 24 volt DC signals may be performed within
another device, such as the traffic controller, an interface unit, or at
the field wire termination panel itself, and processed and compared with
AC voltage measurements within the conflict monitor or another device,
such as the traffic controller or a remotely located computer.
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